jmthunderbirdturbo
jmthunderbirdturbo HalfDork
7/8/20 5:05 a.m.

hey all.


So, 1996 Coachman motor home. Ford E-superduty chassis (14050GVW, AKA F-53 chassis). 460 Gas EFI, Automatic 4 spd, 60,000 miles. When going camping last weekend it stalled out on me in the hills with better than half a tank of fuel in it. I did some reading, and it appears that when the fuel gets overheated, and your pulling a heavy load (it was 95+ and I was towing my 24ft pontoon boat), the fuel pump cavitates or vapor locks, and you lose fuel pressure. After I filled the tank some with the gas can from my boat, then all the way with cold fuel from the Gas station, it ran fine. I plan to drop the tank, replace the sock and pump assembly, and the fuel filter. Here's my question: which pump? I did some research, and read that some of the earlier chassis has different pumps, and those were better, but none of them were 'good', and this issue is kind of common on all sorts of Ford Superduty chassis in the 90s. That led me to a part number for the 'better' pump, which led me to rock auto and amazon, and those pump/hanger kits are like $350... I can't justify spending more on this pump than I did for my 500HP drag car. So then I thought, ok, why not just replace the sock and filter, and put in a Walbro 255 or 340 in the factory hangar like I do in almost every other 80s-90s Ford I own? Finally, someone else on a motor home forum said they had this issue with their MH, and they just replaced the sock and filter, and added an in-line fuel pump on the frame with a secondary relay, and called it good. So what does the hive think about all this?

A - Rockauto/amazon pump assembly and filter and be done with it?

B - Jegs/Walbro GSS340 pump in stock hangar with new sock and filter?

C - Replace the sock and filter, and add an inline pump on a separate relay?

Saron81
Saron81 Reader
7/8/20 6:35 a.m.

I'd recommend the Ford pump, Motorcraft number PFS-48. It'll be expensive, but hopefully a 1 time repair. 

Streetwiseguy
Streetwiseguy MegaDork
7/8/20 6:55 a.m.

A pump mounted outside the tank will work fine most of the time, but they are designed to blow, not suck, so you will potentially have trouble in high temp, low fuel situations.  Early Euro fi applications usually had a large pickup coming out the side of the tank, with a 10mm feed line to the pump, which was mounted low and near the tank.  By the late 70s, most applications had a low pressure feed pump inside the tank, and the larger high pressure pump outside.

So, a cheap low pressure in tank pump feeding your Walbro, or a modified fuel tank with a large feed line coming out of a sump built in the tank should work.  I'd be concerned about knocking stuff off the bottom of the tank, though.

Mr_Asa
Mr_Asa Dork
7/8/20 7:41 a.m.

All of the Ford 4.9L EFI engines had this problem all of the time because of the proximity of the injectors to the exhaust manifolds. 

Ford's answer was to turn up the PSI of the lines.  I forget the exact math, but the normal fuel pressure was something like 36PSI and Ford turned it up to 50-something, doing so made the 14lb injectors act like 16-17lb injectors?  Any possibility you can do something simple like change out the fuel pressure regulator for a higher pressure?

jimbbski
jimbbski SuperDork
7/8/20 8:55 a.m.

The problem is your fuel is heating up.  Most EFI fuel pumps pump more fuel than the engine can use with the pressure reg. sending the excess fuel back to the tank. This heats the fuel up.  Also when the fuel passes through the Reg. is suddenly has the pressure it was under released. The can cause bubbles to form in the fuel. The bubbles are fuel vapor not air but they can cause the cavitation your experiencing. 

Try to figure out where this fuel is dumped back into the tank. Figure out a way to cool the excess fuel as it is forced back to the fuel tank.

I saw a good example of this problem occurr just this past weekend.  I was at the track and a racer was having problems with his car.  After a few laps the car would run as though short of fuel. After talking with the driver and asking about the modifications he had made to his fuel system I suggested he change the location of the return line from the surge tank he was using to the fuel tank. What was happening was this fuel vapor mixture was being dumped into the surge tank, which was fed by gravity from the fuel tank. The fuel pump which was located in the surge tank was picking up this mixture and pumping it up to the engine causing the problem of fuel shortage to the injectors.

jmthunderbirdturbo
jmthunderbirdturbo HalfDork
7/8/20 4:10 p.m.

So, if I were to install an intank walbro for a mustang GT, and then modify the hangar to return the unused fuel away from the pump, I should be fine? 

Where do you get genuine walbro 255s these days?

 

jmthunderbirdturbo
jmthunderbirdturbo HalfDork
7/8/20 6:22 p.m.

So, if I were to install an intank walbro for a mustang GT, and then modify the hangar to return the unused fuel away from the pump, I should be fine? 

Where do you get genuine walbro 255s these days?

The pfs48 doesn't fit my tank. I have the larger rear tank that takes the 6 bolts.

 

Jon

jmthunderbirdturbo
jmthunderbirdturbo HalfDork
7/8/20 9:44 p.m.

In reply to jimbbski :

Update: I got the assembly apart, and it is pretty clear what your are saying is whats occurring. The return line doesn't go back to the tank like most 80s and 90s fords im used to do, it goes back to a small 3-4 cup sleeve that houses the pump. The pump sits inside this sleeve, and fuel comes in from the tank through the sock passively, it is not drawn through the sock, because the sock isn't on the bottom of the pump, it's on the outside of this sleeve. The return line also goes to this sleeve, so the assembly only lets fuel in through the sock when the sleeve runs low from the engine using the fuel. I'm certain this sleeve is filling with emulsified fuel when the temperature and turbulence rises, causing the pump to cavitate, dropping the pressure, making more emulsified fuel, and eventually killing the engine. 

My plan is to cut the bottom off of this sleeve, and mount a new sock on the bottom of a new pump. Then I will modify the return line to point away from the pump assembly, in the event that I do get emulsified fuel again, the entrapped vapors will rise to the surface of the tank, not get drawn back into the pump, hopefully breaking the cycle and keeping the engine running. 

I am looking for a known verified source of Genuine Walbro 255s, so I can order one and get it here. 

Thoughts?

-J0N

Streetwiseguy
Streetwiseguy MegaDork
7/8/20 10:23 p.m.

The reason it feeds back into the sump is because you need it to.  Otherwise, you will starve for fuel below a quarter tank or so, when the fuel sloshed away from the pickup.

Every fuel injected vehicle on the planet ran a system like that until they moved to returnless systems ten or fifteen years ago.  

I believe you are overthinking this.  It's a Ford based system.  The pumps all die exactly in the way you described.  Just put a new pump in the tank, and it will be fine.

jmthunderbirdturbo
jmthunderbirdturbo HalfDork
7/9/20 12:44 a.m.

In reply to Streetwiseguy :

Not to be the guy correcting the people trying to help, but dozens of fords used cannister-less hangars for years, from the early 80s to 2004 or 2005. Mustangs and Fox platform T-birds for sure, as I have owned a dozen of each. Though you may be on to something with low level fuel starvation, I have no intention of running an RV below 1/4 tank anyway, because that's where the generator stops getting fuel.

And I don't believe the pump died, I think it it cavitated, otherwise 6 gallons of fuel wouldn't have fixed it on the side of the road in 100* heat. 

---"I believe you are overthinking this.  It's a Ford based system.  The pumps all die exactly in the way you described.  Just put a new pump in the tank, and it will be fine."--- Maybe, but if it isn't "fine", then what? I have a 1000 mile trip next weekend and a 1800 mile one in august, in the south... I need to be sure. 

 

-J0N

Saron81
Saron81 HalfDork
7/9/20 6:40 a.m.
jmthunderbirdturbo said:

 

The pfs48 doesn't fit my tank. I have the larger rear tank that takes the 6 bolts.

 

Jon

Odd.... Ford lists the same pump and tank on all F53  (75 gallon rear) from 89-97, and the tank and pump both say they're 10 mounting bolts.? 

Streetwiseguy
Streetwiseguy MegaDork
7/9/20 7:37 a.m.

In reply to jmthunderbirdturbo :

Uncrimp the old pumps housing and check the brushes and commutator.  If they are not worn out, I will go with your thought.    

jmthunderbirdturbo
jmthunderbirdturbo HalfDork
7/9/20 4:29 p.m.

In reply to Saron81 :

I saw that, but my tank is 55 gallons, so it's possible this doesn't classify as an F53? Maybe the F53 was class As only?

In reply to jmthunderbirdturbo :

If it's a C Class, it's probably a E350 or E450. Could also be a E Super Duty.

 

jmthunderbirdturbo
jmthunderbirdturbo HalfDork
7/9/20 9:02 p.m.

In reply to Toyman01 (Moderately Supportive Dude) :

It is an E superduty, but finding parts for that specific model has led me to getting the wrong stuff before.

jmthunderbirdturbo
jmthunderbirdturbo HalfDork
7/9/20 9:44 p.m.

Ok, so I bought a Walbro 190LPH pump and sock from Jegs for $75. 190LPH is double the factory spec and about 20% more than the updated assembly you can buy for $350, so it should be plenty of pump. I slightly modified the bottom cannister so the pump isn't drawing ALL its fuel from it, only about half. The sock is now directly on the pump, the bottom of the sock is flat on the tank floor, and the cannister is open to the top of the sock. This should net me decent fuel delivery at very low tank levels, (something I generally refuse to allow, but I suppose anythings possible), and excellent fuel delivery in all other situations. With the cannister not being the source of all the fuel going to the engine, any emulsified fuel should be pushed out of the top of the cannister and rise to the top of the tank, and stay away from the suction end of the pump. This should cure my cavitation issue in the tank. As for the heating of the fuel in the first place, I've decided to header wrap my fuel rails in the engine bay, and as far as I can reach down the trans tunnel. I have the wrap here with the high temp straps, so its a free piece of insurance. Hopefully this will eliminate the fuel from overheating and emulsifying at all. 

Still need to install the new filter, and put the tank back in, but damn is it hot in Ohio this week. 96* today...

-J0N

jimbbski
jimbbski SuperDork
7/10/20 9:31 a.m.

Good luck with those mods.

 

FYI:  The driver of the race car I mentioned in my first post came up to me  on Sunday just before his race.

Where he was having all sorts of running issues on Sat. he now said that the car ran fine in the practice and qualifying sessions that morning.

He made the mods  Sat evening to move the return line to the tank and not the sump he had added.

Toyman01 (Moderately Supportive Dude)
Toyman01 (Moderately Supportive Dude) MegaDork
7/10/20 12:48 p.m.
jmthunderbirdturbo said:

In reply to Toyman01 (Moderately Supportive Dude) :

It is an E superduty, but finding parts for that specific model has led me to getting the wrong stuff before.

You might try Rock Auto. They have the E Superduty split out from the E350 and E450. 

1996 Ford E Superduty

jmthunderbirdturbo
jmthunderbirdturbo HalfDork
7/13/20 12:39 a.m.

Sweet, thanks Toyman.

 

The mod works great. It runs fine around my small town up little hills on just 5 gallons of fuel, with the needle pointing dead at the red "E" mark. I usually start looking for fuel at 1/2, and stop considering price at 1/4 anyway, so I should be good to go. I think I was having issues at startup with bubbles in the fuel, too, as it used to stall the 1st cold start, every time, and no matter what you did with the throttle, you had to let it die once and restart it for it to idle on its own. It has NOT done this the last 3 cold starts. 

 

on to my next issue: The exhaust fell off. yay. 

 

-J0N

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